Axial piston pump



7, 5 E. L. SHAW 2,757,612

AXIAL PISTON PUMP Filed Feb. 20, 1952' 3 Sheets-Sheet 1 IN V EN TOR. EDWIN L. SHAW @TTW 1956 E. L. SHAW 2,757,612

AXIAL PISTON PUMP Filed Feb. 20, 1952 3 Sheets-Sheet 2 INVENTOR. EDWIN L. 5 HAW Aug. 7, 1956 E. L. SHAW AXIAL PISTON PUMP 3 Sheets-Sheet 3 Filed Feb. 20, 1952 INVENTOR. EDWIN L. SHAW BY AXIAL PISTON PUMP Edwin L. haw, Columbus, Ohio, assignor to The Denison Engineering Company, Columbus, Ohio Application February 20, 1952, Serial No. 272,557

Claims. (Cl. 103-5) This invention relates generally to hydraulic apparatus and more particularly to fluid pressure energy translating devices commonly known as fluid pumps and motors.

In still more particular aspects, the invention relates to fluid pumps and motors of the axial piston type in which the pistons are reciprocated to effect the fluid moving operation by cooperation with a swash or cam plate. In some of such fluid pumps and motors, the pistons are provided with hearing shoes which slide on the swash plate during operation of the pump. In some pumps, fluid under pressure is supplied to the shoes to balance the load imposed on the pistons by the fluid being pumped against pressure and thus cause the pistons and shoes to more-or-less float between bodies of fluid under pressure to the end of increasing the efficiency of the pump and the length of its active life. In some installations of these pumps it has been found desirable to supply the inlet of the pump with fluid under booster pressure or build a supplemental pump into the main pump to secure fluid under booster pressure. In such installations it has been found that the efliciency of the pump may be increased by utilizing the booster pressure to effect the movement of the pistons when the chambers therefor communicate with the inlet of the pump. It is, therefore, an object of this invention to construct the pump so that the booster pressure may be secured and utilized in such manner.

Another object of this invention is to provide a fluid pump or motor having a cylinder barrel with'piston chambers which alternately communicate with inlet and outlet ports in a valve plate and which receive pistons which are reciprocated through sliding engagement by means of bearing shoes with a cam plate, the pistons and shoes providing passages to establish communication between the piston chambers and pockets in the shoes whereby fluid under pressure in the piston chambers will be supplied to the shoes to balance loads imposed on the pistons during operation of the pump, means being provided so that the pockets in the shoes will be vented when the piston chambers communicate with the inlet port and fluid under booster pressure in such port will then tend to urge the pistons out of the piston chambers and quickly fill them.

A further object is to provide the pump in the preceding paragraph with piston chambers having booster and high pressure sections and valved passage means to provide for the flow of fluid from the booster section to the high pressure section and from the latter to the outlet, the pump also having a groove in the cam plate with which groove the pockets in the bearing shoes communicate when the high pressure sections of the piston chambers are in communication with the booster sections of the piston chambers; the groove thus serves to vent the bearing shoe pockets and permit the booster pressure to urge the pistons toward the cam plate or outwardly of the piston chambers. I

Further objects and advantages of the present invention will be apparent from the following description, ref erence being had to the accompanying drawings wherein nited States Patent 0 we CC a preferred form of embodiment of the invention is clearly shown.

In the drawings: Fig. 1 is a vertical longitudinal sectional view taken through an axial piston pump formed in accordance with the present invention.

Fig. 2 is a detail horizontal sectional view on an enlarged scale'taken through the pump shown in Fig. 1 on theplane indicated by the line II-ll of such figure.

Fig. 3 is a front elevation of the port plate used 1n the pump shown in Fig. 1.

Fig. 4 is a detail vertical sectional view taken through the pump on the plane indicated by the line lV-IV of Pi 2.

l ig. 5 is a front elevational view of the cam plate employed in the pump shown in Figs. 1 and 2.

Referring more particularly to the drawings the numeral 20 designates an axial piston pump to which the invention has been applied. This pump is of the type shown in the copending application of Cecil E. Adams and Leroy E. Bonnette, Serial No. 234,634, filed June 30, 1951. The pump is described in detail in such application and only the description necessary to facilitate the understanding of the present invention will be given here. The invention is concerned with a pump particularly of the axial piston type in which fluid under booster pressure is supplied to the inlet of certain pumping chambers and then forced into a hydraulic system under a higher pressure. The pump is pressure balanced to offset the load imposed on the pistons and cam plate by the fluid being pumped.

The pump illustrated includes a casing 21 which defines an internal chamber 22 for the reception of a cylinder barrel 23. The casing has a head 24 at one end and a cover 25 atthe opposite end, the latter being provided with bearings 26 to rotatably support a drive shaft 27. This drive shaft has a splined connection with the cylin der barrel 23 so that when the shaft '7 is revolved by a connecting shaft 28 extending from a suitable power source, the cylinder barrel will also be revolved in the chamber 22.

The cylinder barrel is journalled in roller bearings 39 supported by the casing 21 adjacent the rear end of the cylinder barrel, the forward end of this member being disposed in rotary sliding engagement with a port plate 31 carried by the head 24. As in the copending application,

mentioned above, the head 24 has a hollow pintle 32 projecting therefrom into the chamber 22, the pintle being -municate with a recess 38 formed in one side of the pintle 32. The recess 38 extends longitudinally of the pintle and is connected with a recess 4i) formed in the port plate 31.

Recess 40 is enlarged at one side as shown in Fig. 3 to provide an inlet port 41 with which the smaller sections 42 of the piston chambers 37 communicate as the cylinder barrel revolves. These sections 42 also communicate with an arcuate outlet port 43 formed in the valve plate 31 during the revolutions of the cylinder barrel. The sections 42 and the outlet 43 constitute high pressure sections and outlet of the pump. The inlet 4-1 constitutes a booster section, that is, it receives fluid under booster pressure from the larger sections 36 of the piston chambers. The piston chambers 37 receive dual size pistons 44 for reciprocation therein, these pistons serving to draw fluid into the pump through the port 33 in head 24, discharge it under booster pressure into the port 41 in the port plate 31 then draw the fluid from the port 41 and discharge it under high pressure through outlet 43.

To effect the reciprocation of the pistons in the piston chambers, a cam plate mechanism 45 has been provided. This cam plate is adjustable to vary the volume of the pump but since this volume varying mechanism forms no part of the present invention it will not be further described here. The cam plate mechanism 45 includes a cam plate 46 and means for supporting it in an inclined plane. The surface of the cam plate is engaged by pressure balance shoes 47 which are universally connected with the pistons 44. As shown in Fig. 2, the shoes are provided, in the surfaces which engage the cam, with a pocket 48 which receives fluid under pressure through passages 50 and 51, formed in the piston 44 and the shoe, from the high pressure section 42 of the piston chamber. These passages 50 and 51 are so related that a restriction to fluid flow is provided, this restriction causing a pressure drop under certain conditions between fluid in the high pressure sections of the piston chambers and the pockets or recesses in the shoes.

As shown in Fig. the cam plate is provided with an arcuate recess 52 which is so arranged that the pockets 48 will communicate therewith as the shoes slide over the cam plate. The recess 52 is also so located that the pockets 48 will communicate therewith only when the high pressure sections of the piston chambers are in communication with the booster pressure port 41. Due to the communication of the pockets 48 with the recesses 52 the pockets will be vented to the chamber 22 and no pressure or very low pressure only will exist in the pockets 48 when the piston chamber sections 42 communicate with the port 41. When the pump is in operation a certain predetermined pressure will exist in the port 41. This pressure will also exist in the chamber sections 42 then in communication with the port 41 and some of the fluid will flow through the passages 50 and 51 to the pockets 43 and escape therefrom through the recess 52. Due to the restriction in the passages 50 and 51 the inner ends of the small sections of the pistons will be exposed to a force which tends to move the pistons in an outward direction in the piston chambers thus causing the piston shoes to more firmly engage the cam plate. Due to the force applied by the booster pressure, the pistons will tend to move out of the piston chambers more rapidly permitting the chambers to fill with liquid more readily. Of course the rate of movement of the pistons in the chambers is determined by the inclination of the cam plate and the rate of rotation of the cylinder barrel. The force applied by the booster pressure assists in drawing fluid into the larger sections of the piston chambers also. This force also serves to decrease the load applied to the member 53 employed to retain the shoes in engagement with the cam plate. Frequently in pumps of the character shown and described the force applied to the pressure balance shoes to pull the pistons outwardly in the piston chambers when the pump is operated at high speed dislodges the shoes from the pistons. This invention which causes a force to tend to push the piston out of the piston chamber helps to eliminate the tendency for the shoes to be dislodged from the pistons in this manner. It will be obvious from the foregoing that the invention will improve the pump and increase its efficiency. Since the pressure balance shoes are maintained in firm engagement with the cam plate during the suction strokes of the pistons the noise incident to the operation of the pump will be decreased.

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

I claim:

1. A fluid pressure energy translating device comprising a valve plate with spaced inlet and outlet ports; a cylinder barrel with piston chambers disposed with one end in rotary sliding engagement with said valve plate, the piston chambers alternately communicating with said inlet and outlet ports upon relative rotary movement of said cylinder barrel and port plate; pistons disposed for reciprocatory movement in the piston chambers in said cylinder barrel; an inclined cam plate adjacent the other end of the cylinder barrel for controlling the reciprocations of said pistons; pressure balance shoes between said pistons and said cam plate, said shoes having pressure recesses in the surfaces in engagement with said cam plate, said pistons having restricted passages to establish limited communication between said piston chambers and the recesses in said shoes; and means for supplying fluid under pressure to the inlet port in said valve plate, said cam plate being provided with passage means to vent the recesses in said shoes when said piston chambers are in communication with said inlet port.

2. A fluid pressure energy translating device comprising a valve plate with spaced inlet and outlet ports; a cylinder barrel with piston chambers disposed with one end in rotary sliding engagement with said valve plate, the piston chambers alternately communicating with said inlet and outlet ports upon relative rotary movement of said cylinder barrel and port plate; pistons disposed for reciprocatory movement in the piston chambers in said cylinder barrel; an inclined cam plate disposed adjacent the other end of said cylinder barrel for controlling the reciprocations of said pistons; pressure balance shoes carried by said pistons and engaging said cam plate, said shoes having pressure areas exposed to the surface of said cam plate, said pistons having restricted passages to establish limited communication between said piston chambers and the pressure areas on said shoes, and pump means for supplying fluid under pressure to the inlet port in said valve plate, said cam plate having a pressure relief groove to vent the pressure areas of said shoes when said piston chambers communicate with said inlet port.

3. A fluid pressure energy translating device comprising a valve plate with spaced inlet and outlet ports; a cylinder barrel with piston chambers disposed with one end in rotary sliding engagement with said valve plate, the piston chambers alternately communicating with said inlet and outlet ports upon relative rotary movement of said cylinder barrel and port plate; pistons disposed for reciprocatory movement in the piston chambers in said cylinder barrel; an inclined cam plate disposed adjacent the other end of said cylinder barrel for controlling the reciprocations of said pistons; an arcuate groove in said cam plate substantially in registration longitudinally of said pump with said inlet port; pressure balance shoes carried by said pistons and engaging said cam plate, said shoes having pressure areas exposed to the surface of said cam plate, said pistons having restricted passages to establish limited communication between said piston chambers and the pressure areas on said shoes, the groove in said cam plate serving to vent the recesses in said shoes when said piston chambers communicate with said inlet port; and pump means for supplying fluid under pressure to the inlet port in said valve plate.

4. In a fluid pressure energy translating device, a casing having inlet and outlet ports; a cylinder barrel with piston chambers having booster and high pressure sections; valve and passage forming mean in said casing, said last-mentioned means and said cylinder barrel being in relative rotary sliding engagement with one another; pistons with booster and high pressure sections disposed for reciprocation in the chambers in said cylinder barrel, said valve and passage forming means serving upon relative movement between the same and said cylinder to establish communication between said inlet port and the booster sections of said piston chambers, between said booster sections and said high pressure sections and between the latter and said outlet port; a cam plate for imparting reciprocatory movement to said pistons; bearing shoes between said pistons and said cam plate, said shoes having pressure balance areas exposed to said cam plate; passage means establishing limited communication between the high pressure sections of said piston chambers and said pressure balance areas; and fluid passage forming means for venting said pressure balance areas when the high pressure sections of said piston chambers are in communication with said booster sections.

5. A fluid pressure energy translating device comprising a valve plate with spaced inlet and outlet ports; a cylinder barrel with piston chambers disposed with one end in rotary sliding engagement with said valve plate, the piston chambers alternately communicating with said inlet and outlet ports upon relative rotary movement of said cylinder barrel and port plate; pistons disposed for reciprocatory movement in the piston chambers in said cylinder barrel; an inclined cam plate adjacent the other end of the cylinder barrel for controlling the reciprocations of said pistons, said cam plate having a groove coextensive With said inlet port formed therein; pressure balance shoes between said pistons and said cam plate, said shoes having pressure recesses in the surfaces in engagement with said cam plate, said recesses communicating with the groove in said cam plate when said piston chambers communicate with said inlet port, said pistons having restricted passages to establish limited communication between said piston chambers and the recesses in said shoes; and means for supplying fluid under pressure to the inlet port in said valve plate, the recesses in said pressure balance shoes being vented by the groove in said cam plate when the respective piston chambers communicate with said inlet port.

References Cited in the file of this patent UNITED STATES PATENTS Deschamps Sept. 15, 1942 2,608,159 Born Aug. 26, 1952 

